Fuel tank for automobiles with fuel cell drive

ABSTRACT

A fuel tank for motor vehicles which is connected to a supplementary tank containing a flame-coloring additive, where a data recorder causes, in the event of a fault signal, the flame-coloring additive to be added to the fuel tank from the supplementary tank, and a process for adding a flame-coloring additive to the fuel in a fuel tank.

The present invention relates to a fuel tank for motor vehicles which isconnected to a supplementary tank containing a flame-coloring additive,where a data recorder causes, in the event of a fault signal, theflame-coloring additive to be added to the fuel tank from thesupplementary tank, and to a process for adding a flame-coloringadditive to the fuel in the fuel tank.

Fuel cell driven motor vehicles either contain a storage tank forhydrogen or firstly generate hydrogen from alcohols by means of areforming catalyst and then use this hydrogen in a second step in theactual fuel cell to generate electric current for driving the vehicle(see, for example, “Hightech Report '98”, Daimler Benz AG, PublicRelations, 70546 Stuttgart). The latter vehicles, like those driven byconventional internal-combustion engines, require fuel tanks to hold theliquid fuel. However, the alcohols used as fuel, especially methanol andethanol, burn with a pale bluish or virtually invisible flame, incontrast to gasoline or diesel fuels. This property of alcoholsrepresents a considerable safety risk for the operation of motorvehicles having fuel cells. If the tank is damaged in an accident andthe alcohol escapes and ignites, the alcohol flame can remainundetected. People in the vicinity are therefore exposed to considerablerisk due to combustion or explosions. In addition, extinguishing work ismade more difficult.

It is therefore necessary to add flame-coloring additives to fuels forfuel cell driven motor vehicles in order to ensure that flames are seeneasily and rapidly. Flame-coloring additives are known in principle. Forexample, alcohol flames can be colored, for example, usingalcohol-soluble compounds of the alkali and alkaline earth metals and inparticular using boron compounds. Addition of just 0.2% by weight ofethyl borate ensures an intensely green flame. It is also possible touse unsaturated organic compounds, such as aromatics, which tend to formsoot and burn with a luminous flame.

However, a disadvantage of such additives is that, even at lowconcentrations, they completely or partially poison or reduce the lifeof the reforming catalyst which precedes the fuel cell. In addition,some of the additives (for example aromatics) have a toxicity problem,which means that broad use thereof is not readily possible.

FIG. 1 is a schematic drawing of the invention.

It is an object of the present invention to find a way of addingflame-coloring additives to fuels for fuel cell driven motor vehicleswhich does not have the abovementioned disadvantages.

We have found that this object is achieved by a fuel tank (1) which isconnected to a supplementary tank (2) containing a flame-coloringadditive, where a data recorder (3) causes, in the event of a faultsignal generated by accidents or hazardous operating states of thevehicle, the flame-coloring additive to be added to the fuel tank (1)from the supplementary tank (2), and by a process for adding aflame-coloring additive to the fuel in a fuel tank.

The novel fuel tank is made of materials known to the person skilled inthe art and suitable for fuel tanks, for example plastics, such as highdensity polyethylene (HDPE), polyketone (PK), polyamide (PA), multilayercomposite plastic materials or steel or aluminum. Preference is given toHDPE or steel. These said plastic composite materials are preferablythose based on HDPE with a barrier layer of fluorinated polyethylene,ethylene-vinyl alcohol copolymer (EVOH) or polyamide. The outer shape isadvantageously matched perfectly, by methods known to the person skilledin the art, to the vehicle in which the tank is to be installed. Inaccordance with the invention, the fuel tank is connected to asupplementary tank containing a flame-coloring additive. Thesupplementary tank may be installed inside or outside the fuel tank orin its wall. It is preferably installed in the fuel tank. Thesupplementary tank can have any suitable shape. The supplementary tankis sealed so that the fuel and flame-coloring additive do not mix withone another during normal operation of the vehicle. The volume of thesupplementary tank is small compared to the volume of the fuel tank. Ingeneral, the volume is not more than 10% of the volume of the fuel tank.The pressure in the interior of the supplementary tank may correspond tothe external pressure or may be higher. The internal pressure in thesupplementary tank can be matched to the respective design in a suitablemanner by the person skilled in the art. In general, however, theinternal pressure in the supplementary tank is not more than 10 bar.

The novel fuel tank also contains a data recorder which causes, in theevent of a fault signal, the flame-coloring additive to be added to thefuel tank from the supplementary tank. The data recorder comprisessensors which can record fault signals generated by accidents orhazardous operating states of the vehicle. Examples of such events arecollisions of the vehicle with a barrier, collisions with anothervehicle, overturning, fire, excessive temperature in the tank or suddendeceleration of the vehicle. In a preferred embodiment, the sensor isthe sensor already present in motor vehicles of the prior art fortriggering the airbag, which can advantageously also be used for thenovel purpose. It is also possible to use a plurality of data recorders,which can react to different fault signals, optionally interconnected bya logic circuit.

The data recorder causes, in the event of a fault signal, theflame-coloring additive to be added to the fuel tank from thesupplementary tank. The data recorder controls a device which breaks,opens, punctures or cracks the supplementary tank, allowing the additiveto enter the fuel tank and mix with the fuel.

The device can consist, for example, of one or more tensioned boltswhich are released by the sensor and break or puncture the supplementarytank. The device can also comprise, for example, a valve which opens aconnection between the supplementary tank and the fuel tank, allowingthe flame-coloring additive to exit. In this case, it is advantageousfor the supplementary tank to be under pressure.

Although an active, sensor-controlled device is preferred, the presentinvention also covers, however, devices for breaking the supplementarytank by means of passive mechanics, for example a pendulum impactmechanism of suitable design which uses the impact energy occurring as aconsequence of the change in momentum in the event of an accident tobreak the supplementary tank.

A suitable material for the supplementary tank is selected depending onthe device used to add the flame-coloring additive to the fuel tank.Examples of suitable materials are in principle glass, ceramics, metals,for example steel or aluminum, or plastics. It is also selected so thatthe material is compatible with the flame-coloring additive and the fueland is not swollen by the fuel. In devices which break the supplementarytank, it is preferred to use a material which has good fracturebehavior, i.e. is easily broken by an impact. Examples of suitablematerials are glass and ceramics.

The flame-coloring additive is preferably liquid or is used in the formof a solution, in particular an alcoholic solution. Suitable alcoholicsolvents are, for example, methanol, ethanol and isopropanol, ormixtures thereof. Suitable flame-coloring additives essentially consist,for example, of trimethyl borate, triethyl borate, boric acid, sodiumethoxide, sodium methoxide, benzene, toluene, xylene, and solutions ofhigher aromatics. It is also possible to use mixtures for variousflame-coloring additives.

The amount of flame-coloring additive in the supplementary tank is setso that good flame coloring is achieved even if the fuel tank is full.In general, the supplementary tank contains from 0.1 to 5% by weight,preferably from 0.3 to 1% by weight, based on the fuel.

A vehicle equipped with the novel fuel tank has the advantage that theflame-coloring additive only reaches the fuel in the event of anaccident. In an advantageous embodiment of the invention, theflame-coloring additive is added to the fuel only when an event occurswhich also triggers the airbag. This prevents the reforming catalystbeing poisoned in normal vehicle operation. In addition, general use ofadditives in the fuel is avoided, thus reducing fuel costs.

We claim:
 1. A fuel tank for motor vehicles which is connected to asupplementary tank containing a flame-coloring additive, where a datarecorder causes, in the event of a fault signal generated by accidentsor hazardous operating states of the vehicle, the flame-coloringadditive to be added to the fuel tank from the supplementary tank.
 2. Afuel tank as claimed in claim 1, wherein the data recorder is a sensorwhich also triggers a vehicle's airbag.
 3. A fuel tank as claimed inclaim 1, which is made of a material containing a plastic, steel oraluminum, and the supplementary tank containing the flame-coloringadditive is made of a material containing plastic, steel, aluminum,glass or ceramic.
 4. A motor vehicle containing a fuel tank as claimedin claim 1.